Gas discharge devices



1957 w. J. ARROL ETAL GAS DISCHARGE DEVICES Filed Jan. '21, 1954"Iillir'illlll INVENTORS MAL/FM WIWOL,

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1' ATTORNEY United States Patent 6 GAS DISCHARGE DEVICES William J. Arm]and Sidney Jefferson, Abingdon, England, assignors, by mesneassignments, to the United States of America as represented by theUnited States Atomic Energy Commission Application January 21, 1954,Serial No. 405,374

3 Claims. (Cl. 315-54) This invention relates to gas discharge devicessuch as cold cathode tubes.

An object of the invention is to provide a gas discharge device having ahigh dark current and/or stable striking voltage.

When tritium gas is counted in a Geiger-Muller tube filled in the normalway with argon and alcohol, very extensive radioactive contamination ofthe glass walls of the tube occurs. The contamination is not removed byheating to 150 C. and pumping off. It can therefore be assumed that thetritium is attached chemically in some Way to the glass and it may bepresent in hydroxyl groups attached directly to silicon atoms.

According to the present invention tritium gas is introduced into theenvelope of a gas discharge device. As a gas the tritium is etfective asa low energy beta emitter calculated to increase the dark current andstabilise the striking voltage. An electrical discharge in the gasresults in tritium becoming fixed in the surface of the envelope orother solid parts of the device where it is particularly eifective forthe purpose of the invention. It is believed that the dischargedissociates the tritium and that atomic tritium is fixed in the surface.The drawing discloses a sectional view of a diode tube with tritiumtherein.

Two methods in accordance with the invention by which tritium may beintroduced into a gas discharge device will now be described by way ofexample in connection with the manufacture of cold cathode tubes.

A cold cathode tube 1 with electrodes 2 and 3 in position ready fornormal filling is firstly filled with tritium 4 or hydrogen gascontaining tritium of an activity of about 100 micro curies at about aquarter of an atmosphere and an electrodeless discharge is theninitiated by means of a high voltage, high frequency, electrode such asthe point of .a Tesla coil placed near the wall of the tube.Alternatively, the point of the Tesla coil may be placed in contact withthe lead-in wire of one of the electrodes of the tube. Enough tritiumfor the purpose of the invention goes down on the wall or on theelectrodes as the result of the discharge. The remaining tritium is thenpumped oil and the normal process of manufacture is proceeded with.

The amount of tritium fixed in any part of the internal surface of thetube can be influenced to some extent by localising the electrodelessdischarge as by placing the point of the Tesla coil at a selectedposition outside the tube. The maximum amount of tritium is thereforearranged to be fixed in a position nearest and exposed to the dischargegap or gaps of the tube.

2,804,573 Patented Aug. 27, 1957 In the second method, tritium is mixedwith the gases normally used to fill the envelope. The tritium may bediluted with hydrogen according to the amount of hydrogen the particulartype of tube is able to tolerate. If a gettering process is to be usedthe tritium is then fixed in the solid elements of the tube beforegettering, as in the previous example. In some types of cold cathodetube, however, no gettering process is used in which case the initialdischarge to fix the tritium may be dispensed with since the tritium isalmost equally effective either in the gaseous form or in combinationwith the solid elements of the tube.

During the operation of the tube there will, of course, be discharge andthis will effect fixation of the tritium.

The process of the invention produces a device the inside walls of whichemit, with a half-life of 11 years, a continuous stream of very lowenergy beta particles calculated to increase the dark current andstabilise the striking voltage of the device without involving anappreciable health hazard for the manufacturer or user.

The use of tritium has the advantage over the use of other radioactivesubstances in that, being a pure beta emitter, no activity penetratesthe envelope of the tube and no health hazard arises when large numbersof the tubes are stored in bulk.

In the manufacture of tubes by the first of the above methods no healthhazard arises since the tritium remains confined. In the second method,a precaution is necessary with normal filling machines to ensure thatthe header vessel, from which each batch of tubes is filled with gas, isnot vented into the machine shop, after the tubes are sealed-ofi, as isthe usual practice when inert gases are used.

We claim:

1. A method of manufacturing a gas discharge device comprising the stepsof evacuating the envelope of the device, introducing tritium gas intosaid envelope, producing an electrical discharge in the tritium gaswhereby tritium is chemically fixed to 'a surface Within the device,pumping off the remaining tritium gas and filling the envelope with aknown gas filling.

2. A method of manufacturing a gas discharge device comprising the stepsof introducing tritium into the envelope of the device, producing anelectrodeless discharge in the tritium gas by means of a high voltage,high frequency electrode placed adjacent the outside of the envelope ofthe device, causing tritium to be chemically fixed to the inner surfacewithin the device nearest the discharge and evacuating the remainingtritium and filling the tube with known gas fillings.

3. A gas discharge device comprising an envelope, at least an anode andcathode within said envelope, a coating of tritium chemically fixd tothe inner surface of said envelope, said coating being at least over anarea exposed to the discharge gap of the device, and a gas fillingwithin said envelope.

References Cited in the file of this patent UNITED STATES PATENTS2,374,677 Goldstein et a1. May 1, 1945 2,449,961 Treece et al. Sept. 21,1948 2,576,100 Brown Nov. 27, 1951 2,652,510 Landrewy et a1. Sept. 15,1953 2,669,609 Linder Feb. 16, 1954

3. A GAS DISCHARGE DEVICE COMPRISING AN ENVELOPE, AT LEAST AN ANODE ANDCATHODE WITHIN SAID ENVELOPE, A COAT ING OF TRITIUM CHEMICALLY FIXED TOTHE INNER SURFACE OF SAID ENVELOPE, SAID COATING BEING AT LEAST OVER ANAREA